SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS Eduardo Pabuna WESTCO ELECTRICAL
[email protected]
Agenda • Introduction. • Partial Discharge – a precursor to failure. • Radio Frequency Interference (RFI) detection - understanding what we are measuring. • Complimentary EMI detection techniques using different sensors • Case studies • Conclusions
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Key Drivers A successful substation asset management strategy depends heavily on predictive maintenance assessments conducted periodically: Surveillance based techniques to identify potential sites of insulation degradation Followed by more investigative and invasive quantitative techniques
Adds value to the maintenance work, selectively identifying and replacing those items of plant that have deteriorated significantly.
Identifies HV apparatus that presents a potentially safety hazard to staff and public. Cost effective and non expert use. SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
External discharges
Surface discharges caused by pollution on the insulator surfaces.
Leakage currents on insulator surfaces.
Insulator damage.
Corona.
Loose connections
Internal discharges Voids in the insulation. Poor conductor-insulation interfaces.
Metal irregularities/contaminants
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
PDS100 – PD Surveyor PD Detection by RFI/EMI
Partial Discharge (1) • PD occurs when insulation defects exist which produce distorted and enhanced electric field stress.
• Causes of PD in insulation system:
Voids in epoxy resins, polymers, paper Bubbles in liquids/oils Metal depositions/irregularities/contaminants Electrodes and insulation surfaces Poor terminations/loose joints
• Environmental stresses can act to accelerate the deterioration of the insulation system in HV apparatus.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Partial Discharge (2) Can also arise through: Poor design and manufacture Damage of equipment Poor installation processes/workmanship General “ageing” or deterioration of materials Lightening strikes, transients, overloading
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Partial Discharge (3) •
•
PD is a symptom of degradation
Once present – it dominates as it’s own “inherent” stress degradation mechanism
poor preparation poor preparation
erosion traces
• Precursor to complete insulation failure and breakdown
poor preparation
Cable Termination Area
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Detection of partial discharges Detection is based on the energy exchanges that take place during the discharge
Dielectric
losses
Heat
Light
Electromagnetic Chemical changes,
Radiation
gases
Impulse current pulses
Sound/ noise
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
RFI Emissions IEC60270 measurements – Quantify “apparent charge” involved in PD event – Integration of current pulse – Requires physical connection to measure current pulse
RFI measurements – Radiated signals depends on the dynamics of charge motion – Signals generated when charge is accelerated, e.g. • Charge oscillation • Charge movement
– PD current pulse comprises moving charges thus radiation will ensue SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
RFI Case in UK, 1984:
Experience of a transformer fire that followed a bushing failure: During 6 months before this failure neighbors were complaining about Radio & TV interference, foretelling what was coming. Since then, RFI surveys are routine.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Understanding What We Are Measuring
Partial discharge pulse
RFI emission frequency spectrum PD current pulse comprises moving charges thus radiation will ensue It emits an impulsive electromagnetic wave that travels in the surrounding media. SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Understanding What We Are Measuring
Detecting and measuring a partial discharge event is analogous to listening for the strike of the hammer on the bell – at distance what we hear are the resonant harmonics. SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
RFI propagation
discharge source
Amplitude of higher frequency emissions drop of quicker with distance
Source of discharge may be located to an area or specific item of equipment Discharge pulse propagation
Radio frequency, or RF signals, weaken as they travel through free space because of divergence or dispersal, much the same way light travels away from a light bulb. SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
How? • RFI from PD source radiates intermittently • PDS100 scans VHF/UHF in steps of 6 MHz for 1-1000 ms (set by user) • Captures RF energy by amplitude SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Scanning for RFI emissions SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
How? 1. Establish baseline outside substation or switch room 2. Walk from point to point inside substation in service 3. Look for changes in amplitude of the RF-activity 4. If indications of PD – approach the apparatus and see if the activity increases
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Typical RFI spectrum without discharge source (frequency sweep mode)
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Compare Background signal with signal next to source
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Frequency Range Contributions 1) Corona in air around sharp metal will be dominant up to 10 MHz but will go as high as ~250 MHz 1) Surface discharge on dirty porcelains will dominate from 10 to 250 MHz. Heavily influenced by time of year, rain washing etc. 3) PD will extend RFI up to 1GHz on the PDS100 (but actually can go much higher). The higher the frequency the greater the attenuation
Localization of PD requires the using the attenuation to your advantage! The closer you get to the source of PD the more sensitive (elevated) the higher frequencies
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Fault Characterization
Measured impulse events from an arcing discharge source (time resolved mode)
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 1 Survey of Switchyard revealed high RFI in vicinity of Isolator
The time resolved plot shows a typical arcing type discharge
Deviations from Background (Black) becoming larger when approaching the isolator
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 1 Survey of Switchyard revealed high RFI in vicinity of Isolator
• •
•
It was recommended to pay particular attention to the isolator and to look for floating metal parts. Several Cu braids and springs were found to be burned off and just lying in the centre pole enclosure of the isolator. In addition the insulators on the load end (CSBP) were replaced due to glazing damage of the surface due to a previous flashover. A repeat test after repair of the isolator showed no significant deviation from background for all HV plant in this switchyard.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 2 11KV switchboard
During a routine Survey some RFI activity was found in front of only one 11kV switchgear panel.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4 400/275/22kV 800MVA Transformer
• RFI scans performed on places indicated by red dots
L11
L12
Radiator
L13
L3
L4 400 kV L2
275 kV
L5
L1
Tapchanger
L7
L10
L9
L6
L8
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4 400/275/22kV 800MVA Transformer
The PD scans at location L3 and the baseline is shown . The PD measurements showed increases in amplitudes when compared with the baseline measurement indicating evidence of discharge activity. SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4 400/275/22kV 800MVA Transformer
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4 400/275/22kV 800MVA Transformer
•
RFI scan at L8 (TDM at arrow 790MHz)
•
Time domain mode at 780MHz – Pos. L8
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4 400/275/22kV 800MVA Transformer
• Clear signs of severe PD • The transformer failed 2 weeks after this survey
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4 132kV CT
•
Strong RFI emissions were detected in the range of 750 to 900 MHz indicating significant PD activity in the oil dielectric.
•
Further interrogation of RF signals were done in time domain mode at different PD frequencies.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case Study 4 132kV CT
Time Resolved Mode showing correlation with system voltage
DGA results confirm internal PD
C & TD Test data of CT’s insulation measured Tan Delta at 3.0%.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Case 5 – 300 kV - Surge Arrester
RFI measurement was carried out during routine substation survey. • Very high amplitudes at the highest frequencies indicated serious PD. • Other arresters in the same switchyard followed the baseline.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Other decoupling options TEV Joint
Metal Cladding
HV Busbar EM Wave
EM Wave PD TEV Probe
EM Wave
PDS 100 Far-Field Propagation
Photo showing the deployment of a TEV probe
Graphic Showing Transient Earth Voltage Detection of Partial Discharge Activity.
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Other Sensors: High Frequency CT’s
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
UHF Transformer Sensors
UHF Plate Sensors (Mounted in Hatch)
UHF Drain Valve Sensors
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Use of Complementary EMI Couplers
Frequency plot of injected pulse
Using a UHF coupler on a GIS Substation.
Time resolved trace @ 810 MHz
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Example of a Detected GIS Defect
Frequency trace for a floating particle
UHF signal @ 2.5 GSs-1
Time resolved trace @ 871 MHz; -repetition rate 1 s-1
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Summary • Impulsive broadband emissions are a characteristic of insulation defects in HV substations. • The PDS100 instrument platform is specifically designed for substation surveillance and can greatly assist in early stage recognition and reporting of PD. • RFI offers a routine non-invasive and costeffective surveillance technique. SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS
Thank You!
QUESTION?
SUBSTATION SURVEILLANCE USING RADIO FREQUENCY INTERFERENCE (RFI) MEASUREMENTS